1) Field
Embodiments of the invention are in the field of semiconductor processing and, in particular, ammonia-based plasma treatments for metal fill in narrow features.
2) Description of Related Art
For the past several decades, the scaling of features in integrated circuits has been the driving force behind an ever-growing semiconductor industry. Scaling to smaller and smaller features enables increased densities of functional units on the limited real estate of semiconductor chips. For example, shrinking transistor size allows for the incorporation of an increased number of logic and memory devices on a microprocessor, lending to the fabrication of products with increased complexity. Scaling has not been without consequence, however. For example, as the dimensions of the fundamental building blocks of microelectronic circuitry are reduced and as the sheer number of fundamental building blocks fabricated in a given region is increased, the performance requirements of the materials used in these building blocks have become exceedingly demanding. One example is the need to deposit metal films in trenches having high aspect ratios and relatively very small dimensions.
Contacts and vias may be formed by a damascene process. In such a process, a trench is patterned in a dielectric layer and subsequently filled with a metal film. However, as constraints on dimensions increase, problems may arise with conventional filling approaches. For example, FIGS. 1A-1F illustrate cross-sectional views representing operations in a conventional damascene process wherein the dimensions have become too fine for a successful damascene fill.
Referring to FIG. 1A, a patterned dielectric layer 102 is formed above a substrate 100. Patterned dielectric layer 100 has trenches 104 formed therein. A typical patterning scheme used to form patterned dielectric layer 102 may include an etch process (to form trenches 104), an ash process (to oxidize and remove polymers formed during the etch process), and a wet clean process (to remove residues not removed by the ash process). However, residues 106 can be left behind along the surfaces of trench 104, as depicted in FIG. 1A.
Referring to FIG. 1B, a heating process may be carried out in order to remove condensed water (from the wet clean process) or other volatile contaminants. However, certain residues 106, such as polymeric or partially oxidized residues, may not be removed by the heating operation.
Referring to FIG. 1C, a metal barrier layer 108 is deposited over patterned dielectric layer 102 and in trenches 104. However, metal barrier layer 108 may undesirably be deposited over residues 106. Heat treatment of the metal barrier layer 108 is then carried out prior to metal fill of trench 104. Referring to FIG. 1D, this heat treatment may cause residues 106 to volatilize or out-gas (partially volatilize), as depicted by the arrows.
Referring to FIG. 1E, any out-gassing or complete volatilization of residues 106 during the heat treatment of metal barrier layer 108 may cause damage 110 to metal barrier layer 108. Damage 110 may be in the form of non-uniformity of the top surface of metal barrier layer 108 or in the form of craters formed in metal barrier layer 108. Such damage may detrimentally impact a nucleation layer formed on the surface of metal barrier layer 108. Referring to FIG. 1F, a metal layer 112 is deposited above metal barrier layer 108 (or above a nucleation layer which is above barrier layer 108) and in trenches 104. However, voids 114 can be formed within metal layer 112. In particular, trenches 104 may not be completely filled by metal layer 112 as a result of damage 110 in metal barrier layer 108. As the dimensions of trenches 104 are scaled ever-smaller, the relative size of voids 114 in filled trenches 104 becomes more significant and may hinder the performance of contacts or vias formed therefrom.